The present invention generally relates to a personal identification or authentication apparatus using living bodies. More specifically, the present invention is directed an apparatus for authenticating persons while utilizing blood vessel patterns acquired by imaging light which has transmitted through living bodies.
While a great interest has been given to security techniques with respect to personal properties and personal information. Specific attentions have been paid to biometric authentication techniques capable of performing authentication by utilizing living body information of individuals such as finger prints, irises, and veins, as personal authentication techniques having higher utilization. The biometrical authentication techniques have less risk of illegal uses caused by stolen, or lost products. Among these personal authentication techniques, finger vein authentication techniques capable of authenticating individuals by utilizing differences in blood vessel patterns of fingers own the following features. That is, since the finger vein authentication techniques never suppose criminal searches such as fingerprints investigation, the finger vein authentication techniques own less psychological resistance feelings. Also, since internal features of living bodies are utilized, there is a small risk of thefts.
Authentication using finger veins is realized in the below-mentioned manner. That is, when infrared light is illuminated to a finger, the illuminated infrared light is scattered in an interior portion of the finger, and thereafter, is radiated outside the finger. At this time, since hemoglobin contained in blood may largely absorb the infrared light, as compared with peripheral tissue of blood vessels, when the light which has transmitted through the finger is imaged, blood vessels distributed under the skin of this finger, namely, finger veins may be visualized as dark shadow patterns. While feature data of the finger vein patterns acquired from this image has been previously registered, a judgement is made as to whether or not a user corresponds to a registered person by acquiring a correlative relationship between the previously registered feature data and feature data of finger vein patterns which are acquired from an image of a presented finger so as to perform personal authentication.
In conventional finger vein authentication apparatuses, guide units for fixing positions of fingers have been installed therein in order that users can present their fingers in a better repeatability. Since the fingers are presented on the guide units, the repeatability characteristics of images of veins to be imaged are increased, so that high precision authentication can be carried out. Also, since the presentation positions of the fingers become stable, light from light sources can be firmly illuminated to the fingers, so that there is no possibility that strong light is leaked from peripheral portions of the fingers. As a result, sharp vein pattern images can be photographed. However, when authentication is carried out, the conventional finger vein authentication apparatuses must partially contact the own apparatuses to the fingers, and therefore, these conventional finger vein authentication apparatuses can be hardly used under such an environment that sanitation is of particular importance.
As an authentication apparatus capable of solving this problem, a personal authentication apparatus which acquires images of veins in a perfect non-contact manner so as to perform authentication is disclosed in JP-A-2002-83298 (corresponding to U.S. Pat. No. 6,993,160). Since positioning operations of fingers by being actually contacted to guide units cannot be carried out in such non-contact type authentication apparatuses, presentation positions of these fingers are easily varied, so that repeatability characteristics of photographed images are deteriorated. As a consequence, this non-contact type authentication apparatus is equipped with a v for correcting a rotation by employing a contour of a finger within a photographed image, and a unit for normalizing the photographed image while a position of a fingertip is defined as a reference. As a result, even in such a case that the position of the finger within the photographed image is varied, authentication can be correctly carried out.